Derivative Financial Instruments - Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet (Detail) - Copper Swap Contracts [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Net Fair Value - (Liability) Asset	$ 36.0	$ 6.2
Accumulated other comprehensive gain, net of tax	23.0	3.3
Other Current Assets [Member]
Derivative [Line Items]
Net Fair Value - (Liability) Asset	15.5	2.1
Other Assets [Member]
Derivative [Line Items]
Net Fair Value - (Liability) Asset	$ 20.5	$ 4.1

Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558989&loc=d3e80720-113993

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580

Name:	us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration